I got two Honey Sunset Gouramis almost a week ago and found one dead today (which I was thinking he might be near the end because he was so pale looking and lethargic) I've just never had gouramis so I am not familiar with their behavior. But anyways the other one doesn't seem to have any trouble swimming around and being active or even getting food, but over the past few days he (at least I think it's a male) has changed from a nice reddish orange color to a darker more blackish tint.

Here he is the day I got him:

Now this is what they look like:

I'm not really sure where to go from here, or even why he has turned such a drastic color. I thought maybe it was the black substrate that was just making him adapt to the environment or if it was stress related or what.
I have been observing all of them more closely since I've noticed the change but none of my other fish seem to show any signs of illness and all seem to be swimming around happily in the tank.
Thanks for any help!